Handling of NFS4ERR_OP_NOT_IN_SESSION and NFS4ERR_NOT_ONLY_OP errors.

Operations  other than SEQUENCE, BIND_CONN_TO_SESSION, EXCHANGE_ID,
CREATE_SESSION, and DESTROY_SESSION, MUST NOT appear as the first
operation in a COMPOUND.  Such operations MUST yield the error
NFS4ERR_OP_NOT_IN_SESSION if they do appear at the start of a COMPOUND.

If any of CREATE_SESSION, EXCHANGE_ID, DESTROY_SESSION and DESTROY_CLIENTID
are sent without a preceding SEQUENCE op, then it should be the only op in the COMPOUND.